Percussion tool



Dec. 21, 1948. GOLDSCHMIDT 2,456,631

PERCUS S ION TOOL Filed March 19, 1946 3 Sheets-Sheet 2 I/ VEIVTOR R0001 F G01 DEC/WWO):

Dec. 21, 1948. GQLDSCHMIDT 2,456,631

PERCUSSION TOOL Filed- March 19, 1946 3 Sheets-Sheet 3 22 4. uvvevv 47/001 F 601 DSC /M ATTOR/Vfy Patented Dec. 21, 1948 PERCUSSION TOOL Rudolf Goldschmidt, Sheffield, England Application March 19, 1946, Serial No. 655,632 In Great Britain March 22, 1945 14 Claims. 1

This invention relates to mechanically-operated percussion tools, such for example as power hammers, riveters, paving-breakers and rock drills, and it is concerned with means for transforming the rotary motion of a. driving motor into reciprocating motion of a striker co-operating with a tool butt, tool holder or other anvil.

My Patent 2,407,604, dated September 10, 194:6,

relates to such a tool in which the striker is rotatable within a tubular body and is capable of reciprocation along the axis of the body. A motor is drivably connected with the striker for maintaining it in rotation, and the striker includes a centrifugal mass (hereinafter termed a flyweight) constrained to follow the rotation and reciprocation of the striker and capable of bearing under the influence of centrifugal force on the interior surface of the body. This surface is shaped to provide a helical track such that the reaction imposed by the helical track on the fLyweight serves to convert the rotary motion of the striker into translatory motion. The hand of the helical track is such that at the end of its in (working) stroke the flyweight and the track co-operate to wind the striker outwards (i. e. away from the anvil member), the hand of the helical path traced out by the flyweight during its working stroke being opposite to that of the helical track. The dynamic coupling between the striker and the body is accordingly closer during the outstroke than during the instroke of the striker, the change from loose to close coupling taking place with the change in the direction of the translatory motion of the striker after its impacting. Towards the end of the outstroke the translatory motion of the striker is arrested, for example by causing the flyweight to enter a converging race which constrains the flyweight to move towards the axis of the striker against the influence of centrifugal force; thereafter the striker is accelerated on its instroke by the axial component of the reaction of the flyweight on the race.

The present invention provides improvements in and modifications of the invention forming the subject of my said application and among the objects of the present invention are: to provide complete, instead of partial, decoupling between the fiyweight and the helical track during the in-stroke of the striker; to improve the shape of the said helical track; to provide an alternative to the said converging race for reversing the motion of the striker at the end of its outstroke; to enable a high speed of rotation of the striker and consequently a small driving motor to be employed while the impacting frequency of the striker islow and, for a given motor power, the force of each blow is correspondingly large; and to provide means for imparting rotation to the anvil while the tool is operating.

Other objects and advantages of the invention will be apparent from the following description of different embodiments thereof, given with reference to the accompanying drawings, in which-- Figs. 1A and 1B are sectional side elevations respectively of halves of an electrically-driven hand riveter, taken on the line l'l in Fig. 2, the striker being shown at the inner end of its-stroke in Fig. 1A and at the outer end of its stroke in Fig. 13,

Fig. 2 is a section of the whole riveter on the line 2-2 in Fig. 13,

Fig. 3 is a side elevation of the outer end portion of the striker, as viewed in the direction of the arrow 3 in Fig. 2,

Fig. 4 is a diagrammatic development of part of the internal surface of the body of the same tool,

Fig. 5 is a section, on a larger scale, of part of the outer end portion of the striker, taken on the line 5-5 in Fig. 2,

Fig. 6 is a diagrammatic section of a modified form of apparatus in accordance with the invention and intended for use as a rock drill,

Fig. '7 shows diagrammatically in section another modification,

Fig. 8 is an elevation of the striker;

Fig. 9 is an elevation as viewed from the lefthand side of Fig. 8;

Fig. 10 is a plan of the striker;

Fig. 11 is a section of one side of the striker, taken on the line ii-Il of Fig. 9;

Fig. 12 is a section on the line l2-l2 of Fig. 11; and

Fig. 13 is an elevation of the striker head, in the direction of the line A-A of Fig. 10.

The tool has a tubular body shell ID, to the outer end of which is fixed a high-speed electric motor, a portion of which appears at II. This motor has a hollow shaft l2 co-axial with the body. An anvil i3 is slidably fitted in the inner end of the body and carries a riveting snap M. A tubular guide rod I5 extends co-axially within the body ID from the anvil l3 with which it is integral. A shaft I6 also lying co-axially within the body has one end spigoted into the hollow motor shaft i2 to which it is drivably connected by a screwed bush H, the other end of the shaft l6 having an elongated section. A striker including a head portion l8 rigid with a shank I9 is the interior surface diverges slightly,

slidable and rotatable on the guide rod l and is provided with longitudinal keyways engaging the portion of the shaft IS with elongated section. so that the striker is constrained to rotate with the motor shaft l2. 1

The striker head I8 contains two diametrically opposed like fiyweights each in the form of a hardened steel ball 2| surrounded with a small clearance by a hardened steel ring 22 having a peripheral flange 23. The rings 22 are slidable in recesses 24 inclined as shown in Figs. 3 and 8 to 13, the parts of the balls 2| that project from the rings 22 being slidably guided in segmental grooves in the walls of the recesses 24. The outer end of the striker head is cambered, as indicated at 26, the apex 26 (Figs. 3 and 10) of the camber lying along the line A-A in Fig. 2, the broken circle 0 in Fig. 12 represents the profile of a cutter adapted to make the recesses 24.

Within the outer end portion of the body shell I0 is a body liner 2'! having at its outerend an external flange which is secured to the shell ill by screws 28. The interior surface of liner 21 has at its inner end a circumferential idling groove 29 around which the flanges 23 of the fiyweight rings 22 can run when the anvil I3 is fully extended. Beyond the idling groove 29 being frusto-conical as indicated at 30 in Fig. 5. Beyond the diverging portion 30 the interior surface is in the form of a two-start helical grooved track; the grooves being denoted by MA and SIB. The pitch of the track is constant except at the outermost turn, the pitch of which progressively increases, as is evident from the diagrammatic development shown in Fig. 4. At the termination of the grooved tracks near the outer end of the body and bottoms of the groo'ves are of progressively decreasing radius. as shown at 32A and 328, so as to throw the flyweights inwards as the rings 22 leave the ends of the grooves. The body also includes a face cam 33, fixed to the outer end of the body shell III by the screws 28; the cam has two diametrically opposed lobes 34A and 34B. The final lead angle 35 of the helical tracks near the ends 32A and 32B is slightly steeper than the angle of incidence 36 of the backs of the cam lobes. The angle 31 of the fronts of the cam lobes determines the striking velocity, as will be hereinafter explained.

The device operates as follows. The motor H, the direction of rotation of which is shown by the arrow in Fig. 2, is run up while the anvil I3 is fully extended in the position shown in Fig. 1, so that the fiyweight rings 22 roll round the idling groove 29. The striker is now spaced a short distance from the surface of the anvil, as shown in the left-hand half of Fig. 1. When the motor speed is high enough. the riveting snap I4 is applied to the work, so that the anvil l3 displaces the striker outwards, causing the rings 22 to pass from the idling groove 29 to the diverging portion 30 of the inner surface of the liner 21. The reaction due to the centrifugal pressure of the fiyweights on the liner accelerates the striker outwards until the rings 22 engage the inner ends of the helical grooves 3|A and MB respectively. There is now a tight dynamic coupling between the striker and the body. and part of the rotational motion of the striker is converted into translation.

As the striker approaches the outer dead point, the progressively decreasing radius of the end portions 32A and 32B of the helical tracks causes the flyweights to be thrown into the striker head the cam lobes throw the striker inwards at a high velocity proportional to incidence 31 on its working stroke. The inner end of the shank I9 of the striker now strikes the anvil, and the flyweights, on the sudden stopping of the inward movement of the striker, are forced by their inertia against the sides of the recesses 24, the inclination of which is such as to cause the fiyweights to move towards the outer ends of the grooves 25, whereupon centrifugal force again operates to engage the rings 22 with the tapered surface 30, so that the cycle is repeated.

Recoillng of the fiyweights from the recesses 24 and their premature re-engagement with the body liner are prevented by dividing each fiyweight into the two concentric parts 2| and 22 fitted together with the small clearance hereinbefore referred to, whereby the energy which might otherwise cause recoil is expended in very high frequency impacting of the two parts of each fiyweight together.

If either of the fiyweights should happen to be pocketed in its recess when the motor is started, the angular acceleration of the striker will cause the fiyweight to move towards the outer ends of the grooves 25, so that there is no danger of its remaining pocketed. 1

An important feature of the improved tool is that it can have a small high-speed motor while nevertheless the impacting frequency is low and the energy of each impact correspondingly large. The intervals between two successive impacts may be made so long that even a small motor has time enough to accelerate the mass of the striker in its capacity as a flywheel, after discharge of its accumulated energy in its capacity as a hammer. The energy-restoring intervals are made as long as is necessary by selection of a suitable number of turns for the helical tracks. Thus, for example, with a hand tool such as is shown in Fig. 1 fitted with a motor designed to run up to 10,000 R. P. M., an impacting frequency of 500 strokes per minute can be attained if the number of turns of the helical track is of .the order of This frequency, which is also that of the speed pulsations of the motor, depends of course also on the masses involved and the droop of the torque-speed characteristic of the motor. Therefore the impacting frequency and strikin power can be controlled also on the finished percussion tool on the electrical side by a rheostat in series with a series motor.

The slight friction between the striker and the anvil at the moment of impact tends to impart an intermittent rotation to the anvil. Where, however, a more powerful rotational force is required, as in a rock drill, the modification shown in Fig. 6 may be employed. In this construction the liner I21 and the cam I33 are rigidly connected together and rotatable as a whole in the body shell H0, being supported on a bearing spigot 38 at its outer'end and having at its inner end a hollow boss 39 mounted in a bearing 40. The anvil H3 is slidable in and keyed to the boss 39. The remaining parts of this tool are similar to the corresponding parts of Fig. 1. The powerful rotational impulses impressed on the apex of the cam I33 by the cam-follower camber on the striker head H8, owing to the reaction of the inward thrust upon the striker, are transmitted through the liner I21 and the anvil H3 to the drill 4|, so that the cam, the liner, the anvil and the drill will all rotate as one intermittently, and in the same direction as the striker. The speed of rotation and the force exercised adapt themselves automatically to the resistance met by the drill in its work.

An alternative to the cam-and-follower device I for reversin the direction of translatory movement of the striker at the outer end of its stroke is shown in Fig. 7. The mechanism shown in Fig. 7 is in some respects similar to that shown in Fig. 1, and parts in Fig. '7 correspondin to parts in Fig. l are denoted by the same reference numerals plus 200. The inner surface of the body 2! provides a converging race 42 beyond the outer end of the helical grooves 23IA and 23IB, which are here shown as being formed directly in the body. The striker head 2I8 contains, in addition to the flyweights 22l, 222 that co-operate with the helical grooves, a plurality of relatively massive fiyweights consisting of balls 43 and rings 44 which are radially movable in pockets 55 so shaped that the rings 43 are prevented from moving radially outwards far enough to touch the part of the interior surface of the body that contains the helical grooves 23m and 23IB. The upper ends of thesegrooves run at a constant radius onto a converging race it joined to the general surface of the grooved part of the interior surface of the body by a sharply converging belt 4?.

shown in Fig. 1: it forces the heavy flyweights d3, 44 to move towards the axis of rotation against the influence of centrifugal force, theaxial component of the reaction of these iiyweights on the race arresting the translation of the striker M8, M9 while its kinetic energy of translation is converted into additional kinetic energy of rotation as its rotation is accelerated by the tangential component of the reaction of these flyweights on the striker. Thereafter the striker is accelerated on its instroke by an effect which is the opposite of that just described. The lighter fiyweights 22!, 222 are now moving along helical paths of opposite hand to the helical grooves 23IA, 23IB and as they mount the narrow converging belt 41 they are thrown into the inner ends of the pockets 224 in the striker.

I claim:

1. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil,

a motor drivably connected with said striker for maintaining it in rotation, a centrifugal flyweight mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helicalgroove, the direction of rotation of said motor and the hand of said helical groove being such that when said flyweight is engaged with said groove said striker is wound away from said anvil, means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, and means for The converging race 42 does not produce an 1 increase of translatory energy as does the cam maintaining said flyweight out of said groove during substantially the whole of the stroke of said striker towards said anvil.

2. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil. a motor drivably connected with said striker for maintaining it in rotation, a centrifugal flyweight mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such that when said flyweight is engaged with said groove said striker is wound away from said anvil, and means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, the interior surface of said body being so shaped as to constrain-said flyweight, when said striker is in the neighbourhood of its dead point remote from said anvil, to assume a reduced radius of rotation so rapidly that said fiyweight is thrown out of engagement with said groove.

3. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil,

maintaining it in rotation, a centrifugal flyweight slidable in a recess in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such that when said flyweight is engaged with said groove said striker is wound away from said anvil, and means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, the interior surface of said body being so shaped as to constrain said flyweight, when said striker is in the neighbourhood of its dead point remote from said anvil to assume a reduced radius of rotation so rapidly that said flyweight is thrown out of engagement with said groove and so deeply into said recess that the effective component of the centrifugal force acts to retain said flyweight pocketed in said recess, and said recess being so inclined that the arresting of the translatory motion of said striker by said anvil causes said striker to apply to said flyweight a force having a component in the direction initiating the return movement of said flyweight towards re-engagement with the interior surface of said body.

4. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil, a motor drivably connected with said striker for maintaining it in rotation, a centrifugal flyweight slidable in a recess in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such that when said fiyweight is engaged with said groove said striker causes said striker to apply to said fiyweight a force having a component in the direction initiating the return movement of said fiyweight towards re-engagement with the interior surface of' said body.

5. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil, striker for maintaining it in rotation, a centrifugal flyweight including two concentric parts fitted together with clearance, said fiyweight being mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagea motor drivably connected with said ment with said helical groove, the direction of rotation of said motor and the hand of said heli cal grove being such that when said fiyweight is engaged with said groove said striker is wound away from said anvil, and means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, the interior surface of said body being so shaped as to constrain said fiyweight, when said striker is in the neighbourhood of its dead point remote from said anvil, to assume a reduced radius of rotation so rapidly that said fiyweight is thrown out of engagement with said groove, and the clearance between said two fiyweight parts enabling the surplus kinetic energy imparted to said flyweight on its being so thrown out of engagement with said groove to be dissipated by hi h frequency impacting of said parts with each other.

6. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil, a motor drivably connected with said striker for maintaining it in rotation, a centrifugal fiyweight which consists of a ball surrounded by a ring having a periphery shaped to engage in said helical groove and which is mounted in said striker so as to be constrained to follow its rotation and reciprocation but free 'to move at least in part radially under the influence of centrifugal force so as to engage said ring with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such that when said ring is engaged with said groove said striker is wound away from said anvil, means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, and means for maintaining said ring out of said groove during substantially the whole of the stroke of said striker towards said anvil.

'7. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvii, a motor drivably connected with said striker for maintaining it in rotation, a centrifugal fiyweight mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such. that when said flyweight'is engaged with said groove said striker is wound awayfrom said anvil, and co-operating camming surfaces on the interior of said body and on said striker respectively for reversing the translatory motion of said striker at the end of its stroke away from said anvil.

8. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil, a motor drivably connected with said striker for maintaining it in rotation, a centrifugal fiyweight mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such that when said fiyweight is engaged with said groove said striker is wound away from said anvil, co-operating camming surfaces on the interior of said body and on said striker respectively for reversing the translatory motion of said striker at the end of its stroke away from said anvil, and means for maintaining said flyweight out of said groove during substantially the whole of the stroke of said striker towards said anvil.

9. A percussion tool including a tubular body having a helical groove on its interior surface, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil, a motor drivably connected with said striker for maintaining it in rotation, a first centrifugal fiyweight mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially underthe influence of centrifugal force into engagement with said helical groove, a second centrifugal fiyweight mounted on said striker so as to be constrained to follow its rotation and reciprocation and to remain out of engagement with said helical groove, the direction of rotation of said motor and the hand of said helical roove being such that when said first fiyweight is engaged with said groove said striker is wound away from said anvil, a converging race at the end of said body remote from said anvil for constraining said second fiyweight to assume a reduced radius of rotation and thereby to reverse the direction of translation of said striker at the end of its stroke away from said anvil, and means for maintaining said first fiyweight out of said groove during substantially the whole of the stroke of said striker towards said anvil.

10. A percussion tool including a tubular body, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil, said body having on its interior surface a helical groove and a race which is disposed at the end of said groove nearer to said anvil and which diverges in the direction away from said anvil, a motor drivably connected with said strikis wound away from said anvil, means for re-,

versing the translatory motion of said striker at the end ofits stroke away from said anvil, and means for maintaining said fiyweight out of said groove during substantially the whole of the stroke of said striker towards said anvil, said diverging race serving to initiate engagement of said flyweight with said helical groove after impact of said striker on said anvil.

11. A percussion tool including atubular body, an anvil in said body, a striker rotatable within said body and capable of reciprocation along the axis of said body towards and away from said anvil, said body having on its interior surface a helical groove the pitch of which increases towards the end thereof remote from said anvil, a motor drivably connected with said striker for maintaining it in rotation; a centrifugal flyweight mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such that when said flyweight is engaged with said groove said striker is wound away from said anvil, means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, and means for maintaining said flyweight out of said groove during substantially the whole of the stroke of said striker towards said anvil.

12. A percussion too] including a tubular body having a helical groove on its interior surface, an anvil rigid with a guide rod disposed coaxially in said body, a striker rotatable and slidable on said rod, a motor drivably connected with said striker for maintaining it in rotation, a centrifugal flyweight mounted in said striker so as to be constrained to follow its rotation and reclprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, the direction of rotation of said motor and the hand of said helical groove being such that when said flyweight is engaged with said groove said striker is wound away from said anvil, means for reversing the translatory motion of said striker at the end of its stroke away from said anvil, and means for maintaining said flyweight out of said groove during substantially the whole of the stroke of said striker towards said anvil.

13. A percussion drill including a body, a liner rotatable in said body, an anvil including a drill bit and connected to said liner for rotation therewith, said liner having on its interior a helical groove and a camming surface, a striker rotatable within said liner and capable of reciprocation from said anvil, a motor drivably connected with said striker for maintaining it in rotation, a centrifugal flyweight mounted in said striker so as to be constrained to follow its rotation and reciprocation but free to move at least in part radially under the influence of centrifugal force into engagement with said helical groove, thedirection of rotation of said motor and the hand of said helical groove being such that when said flyweight is engaged with said groove said striker is wound away from said anvil, a camming surface on said striker for co-operationwith said camming surface on said liner to reverse the translatory motion of said striker at the end of its stroke away from said anvil, and means for maintaining said flyweight out of said groove during substantially the whole of the stroke of said striker towards said anvil, the reaction at said camming surfaces serving to impart intermittent rotation to said anvil. I

l 14. A percussion tool including a tubular body having two interlaced helical grooves on its interior surface, an anvil slidably mounted in the inner end of said body and rigid with a guide rod extending towards the outer end of said body, an electric motor mounted on the outer end of said body and having a shaft, a striker rotatable and slidable on said guide rod and slidable on but constrained to rotate with said shaft two centrifugal flyweights slidable in recesses in said striker so as to be constrained to" follow its rotation and reciprocation but freeto move at least in part radially under the influence of centrifugal force into engagement with said helical grooves respectively, the direction of rotation of said motor and the hand of said helical grooves being such that when said flywelghts are engaged with said grooves said striker is wound away from said anvil, and co-operating camming surfaces on said body and said striker for reversing the translatory motion of said striker at the end of its stroke away from said anvil, the interior surface of said body being so shaped as to constrain said flyweights, when said striker is in the neighbourhood of the said end of its stroke,

of said body.

RUDOLF GO.

naransncas orran The following references are of record in the die of this patent:

UNITED STATES PATENTS Number Name Date 1,816,104 Weibull July 28, 1931 2,407,804 Goldschmidt Sept. 10, 1946 

